Central forced air systems are commonly used to heat and cool residential and commercial buildings. These systems force air from a central furnace or air conditioner through duct work that carries the air to various rooms or areas of the building. In order for these systems to work efficiently, it is important to minimize the transfer of air between the inside and outside of the building. One draw back of such weather tight building designs is that indoor air quality suffers. Airborne particles are trapped inside the building and accumulate such that the air in today's buildings may be anywhere from 20 to 100 times more polluted than the outdoor air. For obvious reasons, it is undesirable to have high concentrations of particulates, such as dust, pollen and smoke within a building. To combat this accumulation of airborne particulates, it is common practice to mount high efficiency air-filters in the return air duct of a forced air heating or cooling system.
The most commonly utilized filter element is the media filter. Media filters have extensive surface areas and typically comprise a series of folded pleats which capture airborne contaminates by surface loading. The media filter is retained within the return air duct by a filter assembly or cabinet that commonly includes a filter housing and a cover. The filter housing fixedly attaches to the return air duct in such a way that the return air drawn to the central heating or cooling system is forced to pass through the media filter retained within the filter assembly. As the returned air passes through the media filter, the airborne particulates are captured by the filter element so that the air drawn into the central system and dispersed throughout the building is substantially free of unwanted particulates. After an extended period of use, the accumulation of airborne particulates on the media filter begins to restrict air flow through the return air duct, making the central forced air system work harder and less efficiently. Therefore, filter elements must periodically be cleaned or replaced.
To facilitate the replacement of the filter element within the return air duct, filter assemblies preferably provide a means by which the media filter element retained with the filter housing may be replaced without requiring the removal of the filter housing from its fixed attachment within the return air duct. Typically, the filter assemblies include a removable cover that can be disengaged from the housing to enable the user to remove the filter element from the housing and replace it if necessary. The filter assembly is then returned to its operating condition by replacing and reattaching the cover.
Duct-mounted media filters may be installed in the return air duct in numerous ways, depending upon the location chosen for the media filter as well as the orientation of the return air duct in relation to the central forced air system. As those of ordinary skill in the art will readily appreciate, media filters can be installed as an in-line installation, closet installation, up-flow installation, side installation, or horizontal installation. However, many of the prior art media filter assemblies have been designed with a single orientation in mind, thereby requiring the use of a specifically designed media air-filter for the various types of installation orientations.
Despite the type of installation required and the filter assembly design employed, the most common means of installing the media filter housing involves fastening the filter housing at the appropriate location along the return air duct work using standard sheet-metal screws. Commonly, these screws secure the filter housing to the duct work by being screwed through the duct work and directly into the filter housing. It is very important that these screws do not come into contact with the media filter element within the housing because airborne particles will seek out the path of at least resistance through the filter media and, therefore, any puncture, tear, or hole in the media filter will compromise the filter's efficiency. Many prior art devices have attempted to address this installation concern by providing channels within the filter housing into which the screws may be safely inserted. These channels are created by designing the filter housing to be slightly wider than the filter element to be placed therein and providing the filter housing with guide members that center the filter element within the filter housing and offset it from the corners thereof at a distance sufficient to allow the insertion of installation screws.
These guide members are basically L-shaped members attached to the interior of the housing so as to create enclosed rectangular channels along the length of the interior edges of the housing. These channels provide an area into which screws may be inserted to install the housing in the return air duct without damaging the filter element held between the L-shaped members creating the channel. However, in these prior art devices, the size of the screw that may be used to install the housing is limited by the size of the channel, at least when the screw is being inserted into the channel towards the portion of the L-shaped guide member directly abutting the filter element. If the screw used to install the filter housing is longer than the width of the channel, the screw, when fully inserted, will exit the channel and puncture the filter element. Because the size of the channel adds to the width of the filter housing as a whole, in the interest of material cost, the size of the channel is minimized, and most prior art filter housings must be installed with screws around the order of about 1/2 inch in length.
These channels also limit the means by which the filter housing may be installed because they block off internal access to portions of the filter housing thereby requiring that the installment screws be attached to the housing from the outside in. For many installation orientations, it may be desirable to secure the filter housing to the duct and/or central forced air system by fastening the screws to the filter housing from the inside out. Additionally, these L-shaped guide members create two separate channels that run along the length of the housing at the corners thereof, allowing the filter element to directly abut the top and bottom walls of the filter cabinet. Therefore, the placement of installation screws is substantially limited in that screws can only be placed near the edges of the filter housing because placement outside this area, such as at the middle of the top or bottom wall, would cause the screw to puncture the filter element which directly abuts that area.
The prior art filter assembly designs may also be improved from a manufacturing and structural integrity standpoint. Particularly, the prior art L-shaped guide members which form the channels mentioned above are commonly known to be separate members that are welded, riveted or otherwise fastened at the appropriate edge areas of the filter housing. From a manufacturing standpoint, each extra member or structural item that makes up the filter assembly as a whole increases the complexity in assembling the finished product. Also, it should be realized that each individual structural item secured to create the finished filter assembly introduces an attachment means which may fail and thereby compromises the structural integrity of the filter assembly.
In most prior art filter assemblies, the means by which the filter element placed within the filter housing is accessed is simply a sheet-metal filter cover removably attached to a side of the filter housing. As such, the structural integrity of the filter cover is questionable, as is the seal that the filter cover creates between the filter cover and the filter element placed within the filter housing. If the seal between the cover and the filter element is inadequate, a substantial amount of air traveling through the return air duct may avoid passing through the filter element by following a path of least resistance around the filter element and flowing instead between the filter element and the filter cover.
Thus, there exists the need in the art for a filter assembly that allows the filter housing to be installed in the return air duct in a variety of orientations, wherein the screws utilized to install the filter housing may attach to the housing either from the outside in or from the inside out. Also, there is a need in the art for a filter assembly having less individual parts secured together to create the filter housing, such an improved design serving to decrease the complication of manufacturing the housing and increase its structural integrity. The need also exists for an improvement in the structural integrity of the filter cover and the seal which the filter cover creates between itself and the filter element placed within the filter housing.